Department of Chemistry, Graduate School of Science, The University of Tokyo , 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
JST-PRESTO , 4-1-8, Honcho, Kawaguchi, Saitama 332-0012, Japan.
J Am Chem Soc. 2016 May 4;138(17):5666-77. doi: 10.1021/jacs.6b02128. Epub 2016 Apr 19.
Bis(dipyrrinato)metal(II) and tris(dipyrrinato)metal(III) complexes have been regarded as much less useful luminophores than their boron difluoride counterparts (4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes, BODIPYs), especially in polar solvent. We proposed previously that dissymmetry in such metal complexes (i.e., two different dipyrrinato ligands in one molecule) improves their fluorescence quantum efficiencies. In this work, we demonstrate the universality and utility of our methodology by synthesizing eight new dissymmetric bis(dipyrrinato)zinc(II) complexes and comparing them with corresponding symmetric complexes. Single-crystal X-ray diffraction analysis, (1)H and (13)C NMR spectroscopy, and high-resolution mass spectrometry confirm the retention of dissymmetry in both solution and solid states. The dissymmetric complexes all show greater photoluminescence (PL) quantum yields (ϕPL) than the corresponding symmetric complexes, allowing red to near-infrared emissions with large pseudo-Stokes shifts. The best performance achieves a maximum PL wavelength of 671 nm, a pseudo-Stokes shift of 5400 cm(-1), and ϕPL of 0.62-0.72 in toluene (dielectric constant εs = 2.4), dichloromethane (εs = 9.1), acetone (εs = 21.4), and ethanol (εs = 24.3). The large pseudo-Stokes shift is distinctive considering BODIPYs with small Stokes shifts (∼500 cm(-1)), and the ϕPL values are higher than or comparable to those of BODIPYs fluorescing at similar wavelengths. Electrochemistry and density functional theory calculations illustrate that frontier orbital ordering in the dissymmetric complexes meets the condition for efficient PL proposed in our theory.
双（二吡咯烷）金属（II）和三（二吡咯烷）金属（III）配合物被认为不如其硼二氟化物对应物（4,4-二氟-4-硼-3a,4a-二氮杂-s-茚，BODIPYs）有用，尤其是在极性溶剂中。我们之前提出，这种金属配合物的不对称性（即一个分子中两个不同的二吡咯烷配体）可以提高它们的荧光量子效率。在这项工作中，我们通过合成八个新的不对称双（二吡咯烷）锌（II）配合物并将其与相应的对称配合物进行比较，证明了我们方法的普遍性和实用性。单晶 X 射线衍射分析、（1）H 和（13）C NMR 光谱以及高分辨率质谱证实了在溶液和固态中均保持不对称性。不对称配合物的光致发光（PL）量子产率（ϕPL）均高于相应的对称配合物，允许红色至近红外发射，并具有较大的赝斯托克斯位移。最佳性能达到了最大 PL 波长为 671nm，伪斯托克斯位移为 5400cm-1，在甲苯（介电常数 εs = 2.4）、二氯甲烷（εs = 9.1）、丙酮（εs = 21.4）和乙醇（εs = 24.3）中的ϕPL 值为 0.62-0.72。考虑到具有较小斯托克斯位移（∼500cm-1）的 BODIPYs，如此大的伪斯托克斯位移是独特的，并且ϕPL 值高于或可与在相似波长处发射荧光的 BODIPYs 相媲美。电化学和密度泛函理论计算表明，不对称配合物中前沿轨道排序满足我们理论中提出的高效 PL 的条件。
